The interaction of estrogen receptor (ER) complexes with nuclei and chromatin, and the effect of this interaction on gene expression will be investigated in vitro. Attention will be directed to defining specific differences in the interaction when estrogen concentration is raised from physiological to pharmacological levels or when the anti-estrogen tamoxifen is present. The purpose of this investigation will be to elucidate some of the basic steps by which ER can induce changes in gene expression, and then to explain why high estrogen levels or use of tamoxifen results in a blockage of the normal response of cells to estrogen. Specifically, conditions will be established which maximize the interaction of calf ER with nuclear material from calf hormone target tissues and compared to material from nontarget tissues. It will be determined whether there is more than one class of binding affinities of ER to nuclear material under these conditions, and dissociation constants will be measured. Breakdown or turnover of the ER in nuclei will be measured. Binding of ER to chromatin is to be studied. Use of enzyme reagents will enable us to define discrete areas of chromatin that demonstrate ER binding sites. The influence of prior exposure to estrogens on ER binding to chromatin will be assessed. The effects of ER on the activity of DNA polymerase alpha will be characterized, utilizing exogenously added and endogenous DNA templates. Our recent observation of an ATP-induced stimulation of polymerase activity will provide an experimental probe to explore polymerase activity associated with nuclear matrix and the influences thereon of estradiol and ER. Overall, results will reveal the effects of hormone type and level on interaction of ER with chromatin, as well as those hormone-induced structural changes that occur in the chromatin.